A compression ratio refers, in particular in the context of internal combustion engines, to the ratio of the entire cylinder space prior to the compression, that is to say the total volume, to the remaining space after the compression, that is to say the remaining volume. To realize optimum combustion or power values, it is known that the compression ratio can be varied for this purpose. Examples of such reciprocating-piston machines are described in WO 2014/019683 A1, WO 2014/019684 A1, WO 2015/173412 A1 and WO 2015/193437 A1.
In the known reciprocating-piston machines, different compression ratios are realized for example by changing the effective length of the connecting rod, for example by varying the crank radius, the connecting rod length itself, and/or the compression height. For this purpose, use is made of a generally hydraulically operated adjustment mechanism with one or more piston/cylinder support units, the working volumes of which are interconnected by means of a hydraulic circuit operated with engine oil. The hydraulic circuit includes inter alia also a switch for reversing the hydraulic flow direction from one piston/cylinder support unit to the other or from one working volume to the other. Examples of a connecting rod for a reciprocating-piston machine with variable compression ratio can be found in DE 31 48 193A1, DE 197 03 948 01, DE 103 04 686 A1, DE 10 2010 061 360A1, DE 10 2010 061 363A1, DE 10 2011 056 298A1, DE 10 2011 108 790A1, EP 1 424 486A1, EP 1 426 584 B1, WO 2014/019683 A1, WO 2015/082722 A1, WO 2015/104253 A1, WO 2015/173412 A1, WO 2015/173411 A1, WO 2015/155167 A1.
The above-described switch, incorporated into the hydraulic circuit, of the connecting rod commonly has a switchover element in the form of a bolt, which can be transferred from a first switching position, which is defined by a first stop in the connecting rod, into a second switching position (and vice versa), which is defined by a second stop in the connecting rod. In each of the two switching positions, the switchover element projects beyond a different one of the two outer sides of the connecting rod. The two switching positions correspond to different compression ratios.
The transfer of the switchover element of the switch from one switching position into the other is realized, in many embodiments in the prior art, by means of an actuating element, which has two mutually spaced-apart actuating surfaces which each extend in radial planes in relation to the crankshaft central axis. Linear movement of the actuating element parallel to the crankshaft central axis causes the switchover element, when it comes into contact with one of the actuating surfaces, to be displaced, likewise parallel to the crankshaft central axis. The actuating surfaces run in particular at an acute angle with respect to the movement plane of the switchover element in which the latter moves when the connecting rod is moved by the crankshaft.
In tests using in particular reciprocating-piston machines operated at high rotational speeds, it has been found that the transfer of the switchover element from one switching position into the other does not always take place with adequate reliability, which may be the case in particular at rotational speeds above for example 3000 rpm.